task(G1): layout data model - LayoutDefinition type, Yjs layouts map, undo-tracked CRUD in CADDocument

frontend/src/types/cad.types.ts

@@ -72,6 +72,23 @@ export interface BlockDefinition {
   thumbnail?: string;
 }
 
+/**
+ * Layout (Task G1): Papier-/Plot-Seite mit eigenem Viewport aufs Modell.
+ * Persistiert in der Yjs-Map 'layouts' (key = layoutId).
+ */
+export interface LayoutViewport {
+  center: { x: number; y: number };
+  scale: number;
+}
+
+export interface LayoutDefinition {
+  id: string;
+  name: string;
+  viewport: LayoutViewport;
+  /** Referenz auf den Titelblock-Block (frame block), optional. */
+  frameBlockRef?: string;
+}
+
 export interface BoundingBox {
   minX: number;
   minY: number;